Skill Level: Beginner
Triple Axis Magnetometer - HMC5883L
Breakout Quickstart Guide
by JordanDee | June 30, 2011 |
Overview:
This is a breakout board for Honeywell's HMC5883L, a 3-axis magnetometer.
Magnetometers have a wide range of uses. The most common include using the chip
as a digital compass to sense direction or using them to detect ferrous (magnetic)
metals.
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Triple Axis Magnetometer Breakout - HMC5883L
Requirements:
This breakout board can be hooked up to a number of microcontrollers, as long as
they have an I C interface . However, for this guide you will find the following helpful:
• Arduino Uno
• Breadboard
• soldering iron
• solder
• male headers or other connection method
• (optional) needle nose pliers
• (optional) third hand
How it Works:
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Magnetic fields and current go hand-in-hand. When current flows through a wire, a
magnetic field is created. This is the basic principle behind electromagnets. This is
also the principle used to measure magnetic fields with a magnetometer. The
direction of Earth's magnetic fields affects the flow of electrons in the sensor, and
those changes in current can be measured and calculated to derive a compass
heading or other useful information.
How to Use it:
So you're ready to start using this chip with your Arduino are you? Well lucky for you,
we have everything you need to get your project rolling.
Hardware:
First we'll need to solder on some headers to the breakout board so it will fit into a
breadboard. For soldering suggestions, this tutorial is helpful.
The breakout board includes the HMC5883 sensor and all filtering capacitors
necessary. There are two unpopulated pads in case you need pull up resistors (no
need for them if you're using the Arduino/ATmega328).
Communication with the HMC5883 is simple and all done through an I C interface.
We will go into this in further detail momentarily. All you need to know for now is how
to wire it up. Attach the SDA line to A4 and the SCL line to A5. Also attach Vcc to
3.3V and GND to GND.
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Software:
If you haven't done so already, please download and install the Arduino IDE.
Firmware:
The HMC5883L speaks a kind of funky serial language called I C. I C requires just
two wires for communication – one for a clock (SCL), and one for data (SDA). Be
aware that you probably should avoid using those two pins for anything else (except
for maybe other I C devices, if you want to get tricky). Don't try using them as analog
inputs!
The Arduino code example we have, HMC5883.pde, will continuously reads data from
the magnetometer for each of the magnetometer's axes using I C. If you need help
uploading the sketch to your Arduino, their site has lots of helpful information.
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Let's take a look at the first part of the code:
#include <Wire.h> //I2C Arduino Library
#define address 0x1E //0011110b, I2C 7bit address of HMC5883
void setup(){
//Initialize Serial and I2C communications
Serial.begin(9600);
Wire.begin();
//Put the HMC5883 IC into the correct operating mode
Wire.beginTransmission(address); //open communication with HMC
5883
Wire.send(0x02); //select mode register
Wire.send(0x00); //continuous measurement mode
Wire.endTransmission();
}
The code that resides within the setup() function is ran once at the beginning. It
initializes the serial communication at 9600 baud. We use the serial communication to
send data for each axis back to the computer. The I2C is also initialized. We then do
a 'write' operation to the HMC5883L. The purpose of this 'write' operation is to adjust
the value in the configuration register of the HMC5883L to tell it to be in continuous
operation mode. This lets us make continuous reads of the axis data. By default the
chip is in single read mode meaning after reading from it once, it will go idle to save
power. Once idle, we have write to it to turn it on before we can read from it again.
The datasheet has all the information about the registers in addition to other useful
information. Of course, we always encourage you to RTFM... just look at the
datasheet...
Moving on, here's where we actually request and receive the data:
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The loop() function will run over and over again as long as the board has power. Each
time through, we do a quick write to tell it where we want to begin reading the data for
the axes. Register 3 is selected and happens to be the most significant byte of the X
axis. We request to read 6 bytes one by one. The chip auto-increments the number of
which register we are reading from so we don't have to select each register manually
before we read from it. The x, y, and z axis data is then sent back serially to the
computer. You can see these values by using the 'Serial Monitor' of the Arduino
development environment as shown below.
All you need now is a creative idea of how to use this information in your next project.
Always feel free to share it with us, it just might end up on the Sparkfun homepage!
Resources:
• Schematic
• HMC5883L Datasheet
• Arduino Code
• Example C code (ATmega328)
• Digital Compass How-To Video
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Conclusion:
Enjoy your new magnetometer! If you have any problems, feel free to contact SparkFun Technical
Support at techsupport@sparkfun.com
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